Glial cells monitor and respond to neural activity by conditioning the extacellular milieu, signaling within glial cell networks, as well as by sending signals back to neurons. Unlike neurons, which use electrical signals to communicate, glial cells possess a form of Ca2+ based excitability, where they generate and propagate intracellular Ca2+ signals as waves over long distances in response to synaptic activity. We aim to understand the nature of these signals in glial cells. One objective is to understand the processes that support temporal and spatial characteristics of Ca2+ signals within glial cells and to gain insight into their role in brain function. A second objective is to characterize the specific signal traffic between myelinating Schwann cells and the axons they myelinate in peripheral nerves. Myelinating Schwann cells monitor and respond to impulse traffic along the axons they myelinate. To enable direct measurement of glial cell Ca2+ signals both in astrocytes in the central nervous system and Schwann cells in the peripheral nervous system, we recently developed a transgenic mouse lines that express a fluorescent Ca2+ indicator photoprotein derived from GFP mutants selectively in astrocytes and Schwann cells. Cell specific expression of YC 3.60 was achieved by targeting expression of the DNA construct using the S-100&#61538; promoter, which is selectively expressed in astrocytes and Schwann cells in situ. Immunocytochemical localization revealed robust cell specific expression of the YC 3.60 protein in most astrocytes and all Schwann cells. In addition, native fluorescence of the photoprotein was easily detected by confocal fluorescence microscopy. Two-photon confocal microscopy using infrared illumination enabled imaging of labeled cells deep (500 to 700 m) within tissue. Using the isolated brain slice preparation astrocytic signaling was recorded evoked by neural activity elicited by direct stimulation of identified neural pathways. Similarly, isolated peripheral nerve preparation was used to image photoprotein fluorescence in Schwann cells. The Section had previously characterized the distribution of Ca2+ signaling proteins in the nodes of Ranvier, internodes and the axoglial apparatus in the sciatic nerves, a model peripheral nerve. A characteristic distribution of IP3Rs presumably dictated by the unique architecture of the myelin sheaths around the axons in the nodes and internodes was discovered. Efforts are underway to record glial cell signals in the anaesthetized intact mice using multi-photon confocal microscopy. These experiments are expected to reveal glial cell Ca2+ signals associated with physiological function in the brain and peripheral nerves. This information will be utilized to investigate the alterations in glial cell signaling in pathological states in the brain and peripheral nerves. A newly developed brighter and more robust calcium senson photoprotein indicator is being targeted to glial cells to improve signal-to-noise in recordings of calcium signals in situ.